If you made a course that you want to remove, you can easily delete the course. Note that deleting the course will really delete the course, so there is no going back.
If you just want to remove the course from your list of active courses you can also consider archiving the course instead.
How to delete a course
You should first navigate into the course you want to delete. Clicking on the context menu in the top left corner will show you a menu with the option to "Delete course".